Donald Trump: 'My Republican debate is affecting the polls'

Donald Trump has insisted that his upcoming Republican presidential debate is having an effect on the candidates' poll numbers.

The Celebrity Apprentice star is to host a Republican debate ahead of the Iowa Caucus on December 27, but so far only two candidates have agreed to appear.

GOP frontrunner Newt Gingrich and Pennsylvania Senator Rick Santorum will discuss current events with Trump in Des Moines, while Mitt Romney, Rick Perry, Michele Bachmann and other candidates have declined his invitation.

Trump appeared to take credit for both Gingrich's sudden rise in the polls and former frontrunner Romney's drop in support in an interview with Fox and Friends.

"[Romney's] numbers have gone down very substantially since he said 'no', and a lot people think it's because it showed a lack of decisiveness or a lack of courage in going into this debate," Trump insisted.

The mogul added: "And you look at what happened with Newt. Newt has gone up like a rocket ship [since he agreed to my debate]."